The present invention relates to a D/A converter system which converts a digital signal to an to analog signal.
The conventional D/A converter system has the following problems. That is, since a high precision analog circuit is required to convert a PCM (Pulse Coded Modulation) signal directly in an analog signal, the D/A converter system is expensive. Besides, since the D/A converter is composed of analog circuits, it is difficult to construct the converter on the same ship as signal-processing digital block. The D/A converter must be constructed on an independent chip.
Conventionally, a pulse width modulation system is popular for the D/A converter composed of digital circuits. However, pulse of different widths have different frequency spectrums. Therefore, when an analog signal is reproduced by pulses with different widths, the difference in the spectrum of the pulses causes noise. It means that an analog signal with a good S/N ratio cannot be obtained by the pulse width modulation system.